The proposed research is based on the investigators' prior studies which found that surgical patients undergo disruption of their biological (circadian) rhythms following surgery and hospitalization. The more disrupted patients appeared to recover their rhythmicity at a slower rate than those with less disruption. Using an animal model, the rate of recovery following surgery was studied in relation to the degree of disruption, as well as to the rate at which rhythmicity was restored. The purposes of this study are: (1) To develop a pre-surgical protocol, using an animal model, which will prevent or minimize circadian disruption following surgery; (2) To test the effects of this pre-surgical protocol on a nonhuman animal model; (3) To test the use of the pre-surgical protocol on healthy human subjects; (4) To test the pre-surgical protocol in a human surgical population and to measure its effects on resulting circadian disruption. In the first series of experiments, various schedules of meal timing, exercise, rest/activity, and caffeine ingestion will be tested. A combination of the schedules will be developed which optimally alters the circadian rhythmicity in the normal individual in a pattern which will pre-adjust the individual before surgery in a manner similar to that developed for transmeridian flight by Ehret, Groh, Meinert (1980). In a series of parallel experiments, compliance with the self-measurement of biological rhythms (autorhythmometry) and compliance with the pre-surgical protocol will be tested. Finally, the pre-surgical protocol will be tested on a group of surgical patients to determine its effectiveness in preventing circadian disruption following surgery and in the recovery and restoration of rhythmic synchrony. Implementation of this protocol is expected to improve patient well-being and speed recovery.